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Looking through the tlog, at 117sec the ‘throttle’ (graph this) seems stuck above 80 units. While the speed is high the height is not increasing much but after the slowdown to 2 m/s this excess throttle makes it climb.

Looking at your tlog, it shows your distance to home at 250000 or something silly like that? suggesting the home point was not set correctly or there was an error with GPS?. You need to look at the dataflash files or post them here, to get a better idea of what happened..

Thanks for taking a look Dean. I have had quite a few flights today, getting ever more adventurous and the last one had a speed change 10m/s to 2 m/s like the problem flight but all seemed OK today. On occasions it did seem reluctant to descend though so I increased the IMAX alt hold from 3 to 4. (not really sure what Im doing but it seemed to improve things) As far as I can see there is no parameter for descent rate.

I dont really want to turn this issue into a general shout for copter help but, auto land sometimes doesn’t quite touchdown and then climbs to ‘home’ or descends too fast, sometimes with drift. Also ‘takeoff’ wont take off in auto unless I’m already hovering. Cant find any info on that.

By the way Dean, I dont have sonar, but was thinking it may help with the landing?

I thought you had sonar as it was showing in the log file you posted? check it is turned off in hardware options... If you are using an open board i.e apm 1 or 2 make sure the air pressure sensor is covered with some cotton wool or something so that the wind or prop wash doesn`t affect the altitude. the altitude parameters and throttle will affect auto landing, You can get the machine to auto takeoff but it requires messing around or at least the last time I tries on arducopter 2.5 or 6 it did? it is possible though but requires making an error to take off and then the I term corrects the error in flight.. Probably sounds a bit confusing?

Now I run a business for aerial photography and cinematography although I dont use Arducopter for it as the kit costs around 10k a machine, so reliability and accuracy is very important, the APM will get there one day, and although it improves fairly quickly with time it isnt there yet, but a great tool for learning how these things work and how to fly.. The expesive stuff that I fly can get a little boring, so I get out a KK board or an APM to keep my hand in :) I plan to get another copter soon to put an APM on and get up to date with progress.

I have looked at your logs and I have some feedback. This does look like the effect I was talking about but I suspect the real problem was your tuning of roll and pitch. This is the most aggressive tune I have seen so far.

Stab_P = 7.5 (This is massive, I would stick to 4.5 on all Stab P terms)

Rate_P = 0.17 (Large but might be ok)

Rate_I = 0.01 (too small, should be as large as Rate_P or bigger)

Rate_D = 0.004 (good number)

I think you have tuned this to a whisker away from stable and the copter started to oscillate as you descended. The roll and pitch input you gave in the last second seems to be the final straw and it let go.

I would suggest that you leave the Stab_P terms all the same at 4.5. I would also re tune the Rate P term with the Rate I term at 0.1. Then once you have finished tuning Rate P, I would make sure that Rate I is the same size or larger. You may also consider reducing the Rate P by 25% if you are tuning to near unstable.

After tuning I do a number of tests.

1. Full Roll input and let go of the sticks. (No motor oscillation should be heard)

2. Repeat 1 for Pitch and Yaw.

3. Repeat 1 and 2 in fast climb at 3/4 throttle.

4. Fast decent on near zero throttle for 5m followed by full throttle (all at about 30m+)

5. Fast forward flight followed by leveling and applying full yaw (all at about 30m+)

6. Fast shuttle runs with full Roll and Yaw input at each end. (all at.... you get it)

If you can do these things without any problems you probably have a very good tune. With large props you may still have a good tune but not have the power in the motors to cope with the more extreme maneuvers. The large prop problem should be seen in 6 as the copter falling out of turns and maybe bucking.